The invention concerns a method to control the print process in a printer or copier in which a character generator generates a latent print image and a latent toner marking on an intermediate carrier. Furthermore, the invention concerns a device to implement the method.
To generate the printed image in electrographically operating printers or copiers, toner material is applied and fixed to a carrier material, for example paper, corresponding to the image structure. Examples for such print processes are the electrophotographic method and the magneto-electric method. Here, a latent print image is initially generated on an intermediate carrier (for example on a photoconductor), this latent print image is inked, and subsequently is transferred to the carrier. To achieve a high print quality, the inking of the print image must be kept within narrow predetermined limits. Such a print image can comprise whole surfaces, rastered semi-tone surfaces, lines, characters and other relatively complex image elements. For precise control of the print process, the inking degree for the print image is indirectly determined using a toner marking, and the print process is controlled or regulated dependent on the print result given this toner marking. Therefore, a latent toner marking is generated on the intermediate carrier in addition to the latent image important to the client. Such a toner marking is relatively small compared to the surface of the print image.
Given high color densities or inking degrees, a high concentration of the colorant is necessary, meaning the associated toner marking is relatively dark. Given the scanning of such a dark toner marking by an optical reflection sensor, its sensitivity is reduced, meaning the characteristic line of the color density on the toner marking over the toner concentration runs relatively flat. This has the result that, given high color densities, the adjustment of the precise toner concentration is difficult. This effect is further amplified in that small surfaces are inked darker than large surfaces, meaning the relatively small toner marks are inked darker than the larger surface elements of the print image.
DE-A-39 38 354 specifies a method to control the print process in an image generation device. Given the generation of a latent toner marking, the energy is lowered in comparison to the energy for the generation of a latent print image. A reflection sensor determines the color density of the inked toner marking. Dependent on this signal of this reflection sensor, either the lamp voltage of the character generator, the bias voltage for a development process, or the grid voltage of the main charger is adjusted. The influencing of the toner concentration in the development station is not specified.
The document WO 99/36834 by the same applicant specifies the scanning of toner marks with the aid of a reflex sensor. Dependent on the measurement result of the reflex sensor, the toner concentration in the developer station is adjusted.
The document DE-A-199 00 164 by the same applicant specifies the measurement of the toner density of a toner marking. The toner concentration is adjusted dependent on the measured value.
The document U.S. Pat. No. 4,962,407 specifies an electrophotographic copier device, whereby measurement signals of two reference markings of different color density are used to determine the toner concentration. The toner concentration is inferred from the difference signal for both toner markings, and given deviation from a desired value the toner concentration is corrected in the developer station.
The documents DE-A-41 26 446 and DE-A-41 26 457 specify a developing unit to develop color toner images, in that image patterns that were generated with the aid of two different potentials are scanned. Using the measurement signals, the toner concentration can then be inferred, and these can be updated.